It wouldn't be understood as "what did I miss?". But it also shouldn't be taken too literally - here are just a few examples from the NEID of os cionn meaning "over" or "above", rather that "over head":
"books were stacked on the table" - bhí leabhair carntha os cionn a chéile ar an mbord
"superimposed layers" - sraitheanna os cionn a chéile
"fines in excess of €1000" - fíneálacha os cionn €1000
"to marry above your station" - pósadh os cionn do chéimíochta
"half the population is above sixty" - tá leath an daonra os cionn seasca
"dawn broke over the hills" - d'éirigh an ghrian os cionn na gcnoc